Adherent cells have conventionally been grown on glass surfaces or on polymer substrates. The surfaces for cell culture are often pre-treated to enhance cell adhesion and proliferation. Flasks, plates, and Petri-dishes are commonly used for cell culture in laboratories. For industrial-scale cell culture, such as in the bioprocess industry, the use of microcarriers for cell attachment and proliferation is common. These microcarriers are typically beads or disks with dimensions in the hundreds of micrometers range.
Cultured cells may be detached or released from cell culture supports by a variety of methods. Commonly used cell release methods comprise mechanical methods (such as scraping), treatment with proteolytic enzymes (such as trypsin), the use of calcium chelators (such as EDTA), or a combination of such methods. However, many of these conventional cell release methods can cause adverse effects on cultured cells, and may modify their inherent structure and function. For example, treatment of cells with trypsin (trypsinization) is a harsh method, and is not desirable for delicate cells such as stem cells, due to its potential effect on cell phenotype. Trypsin is typically derived from animals, and may contain impurities like co-fractionated proteins or biological agents such as viruses and mycoplasma . Impurities of animal origin may limit the use of released cells for critical applications such as cell therapy. Mechanical methods of cell release are labor intensive and are impractical for industrial-scale cell culture applications.
Thermoresponsive polymers (TRPs) have recently been used as supports for culturing adherent cells. For example, poly N-isopropyl acrylamide (PNIPAM) has been used as coating for cell culture supports to provide a gentle mechanism for releasing cultured cells. TRPs undergo a sol-to-gel transition when the temperature is raised above lower critical solution temperature (LCST). When the TRP is above its LCST, it forms a collapsed gel or precipitated phase, on which cells can adhere and proliferate. Lowering the temperature of the cell culture system below the LCST stimulates a physical change (swelling/hydration) in the TRP and imparts greater hydrophilicity, which causes a triggered release of the cultured cells. The use of polyelectrolyte-coated TRPs has recently been demonstrated. For example, NIPAM-containing polyelectrolyte multilayer coatings have been used as cell culture supports. These supports were prepared by coating a glass substrate with alternate layers of negatively charged polystyrene sulfonate-co-poly N-isopropyl acrylamide (PSS-co-PNIPAM) and positively charged polyallylamine hydrochloride-co-poly N-isopropyl acrylamide (PAH-co-PNIPAM) copolymers.
Efficient cell release is particularly important for high yield in industrial scale cell culture processes. So, there is an emerging need to develop better cell culture supports for efficient cell attachment and proliferation. Gentle cell release methods to detach the cultured cells from such cell culture supports are also needed.